1. Field of the Invention
The present invention relates generally to an output device for a power tool which can output pure rotation, rotation in the forward direction and axial vibration or rotation in the reverse direction without axial vibration, so as to protect a ratchet gear of the output device from damage.
2. The Prior Arts
A conventional power tool, such as a power drill, generally outputs power from the motor to the output shaft by the gear unit. Besides, in order to tighten the bolts or to loosen the bolts, some power tools are equipped with an axial vibration function which can output an impact force to tighten the bolts or loosen the bolts.
The conventional impact power tool with the vibration function generally comprises an output shaft, a stationary ratchet gear and a movable ratchet gear mounted to the output shaft, at least one block located between the stationary ratchet gear and the movable ratchet gear, a case for accommodating the parts mentioned above, and an adjusting knob which is threadedly connected to the case. The stationary ratchet gear is cooperated with a bearing and located within the case and is rotatable relative to the case. The movable ratchet gear is fixed to the output shaft and is co-rotated with the output shaft. When the adjusting knob is rotated in the forward direction or the reverse direction, the block is controlled to move axially toward the front end or the rear end of the case so as to control the protrusions on the block to be engaged with or disengaged from the ribs on the stationary ratchet gear. When the protrusions are not engaged with the ribs and the output shaft is applied by an axial force to engage the movable ratchet gear with the stationary ratchet gear, because the stationary ratchet gear is free to rotate, the output shaft driven by the power source device provides the output in the form of pure rotation. When the protrusions are engaged with the ribs and the output shaft is applied by the axial force to engage the movable ratchet gear with the stationary ratchet gear, because the stationary gear is fixed, so that the power source device drives the output shaft to rotate and the ratchet teeth on the movable ratchet gear are forced to move over the ratchet teeth on the stationary ratchet gear. By the interference, the output shaft outputs axial vibration.
The disadvantages of the conventional design is that when the protrusions of the block are engaged with the ribs of the stationary ratchet gear, the output shaft is applied by the axial force and rotates in the reverse direction (restricted direction of the ratchet teeth), the movable ratchet teeth and the stationary ratchet teeth will catch against the steeply sloped edges of the teeth. The mechanical stress is very high and therefore the movable ratchet teeth and the stationary ratchet teeth are very likely to break.